Sadao Tsutsumi

Calcium phosphate clusters

The potential energy surfaces associated with [Ca3(PO4)2n clusters are analyzed in detail using ab initio calculations for n ranging from one to four. Considering separated clusters, energy criteria favor the so-called Posners cluster Ca9(PO4)6, which is the core of the actual structural model of amorphous calcium phosphate. This is rationalized through the existence of a distinct CaO bonding pattern in this cluster. Considering aggregated clusters as a possible model for amorphous calcium phosphate, the aggregation of Ca3(PO4)2 clusters appears as an alternative to Posners hypothesis.

Solubility product of OH-carbonated hydroxyapatite

Information on the solubility of OH-carbonated hydroxyapatite, Ca10(PO4)6(CO3)x(OH)2-2x, previously has not been available. In the present study the solubility product (Ksp) of OH-carbonated hydroxyapatite was measured in a 0.1 M acetic acid and sodium acetate buffer solution in a pH range of 4.0-5.8 at a CO2 partial pressure of 10(-3.52) atm. The equilibrium solubility increased with the increase of carbonate content. The Ksp values decreased with the decrease of pH. For example, Ksps were 10(-119), 10(-123), and 10(-130) for pure hydroxyapatite at pH 4.9, 4.5, and 4.1, respectively. The decrease of Ksp was not accounted for by calcium-carbonate complexation. Ksp measured at isoelectric points (L) was expressed as pL = 118.65 - 0.47316 x (CO2 wt%)2.4176. From this formula, the L values were calculated for pure and fully carbonated hydroxyapatite as 10(-118.7) and 10(102.8), respectively. The L value for pure hydroxyapatite agreed with values measured under carbonate-free conditions. Therefore, the L values were regarded as the Ksp for OH-carbonated hydroxyapatite excluding errors arising from carbonate contamination in the solution.

Hydrothermal growth of carbonate-containing hydroxyapatite single crystals

Single crystals of carbonate-containing hydroxyapatite have been grown hydrothermally by gradually heating with a temperature gradient applied to the vessel, using CaHPO4, H2O and carbon dioxide as dry ice. The optimum conditions to obtain large single crystals are: CaHPO4, 10 g/l; final temperature gradient, 33.5°C/cm; heating rate, 0.005°C/min; and carbon dioxide, 55 g/l. The largest crystal obtained was 12 mm in length and 200 μm in width. The CaP molar ratio and the CO2 content of the single crystals were ranging from 1.60 to 1.67 and 0.09 to 0.65 wt%, respectively. Carbonate groups substituted only for OH groups.

Mechanical Properties of Hydroxyapatite and OH-carbonated Hydroxyapatite Single Crystals

Single-crystal hydroxyapatite and OH-carbonated hydroxyapatite have bending strength much higher than that of dense hydroxyapatite ceramic, indicating potential applicability to a load-bearing biomaterial. However, the effects of carbonate on the strength are less clear. The objective of the present study was to determine the bending strength and Youngs modulus of these single crystals with carbonate contents from 0 to 0.62 in CO2 wt%. Three-point bending tests were performed by means of a modified ultramicrohardness tester with a span of 380 μm and a bending direction <210> of the single crystals. The crystals were broken in air, water, and air after immersion in a cell culture medium for 3 wks. The average Youngs modulus of the single crystals was from 54 to 79 GPa. The average bending strength of the single crystals in air was 500 ± 184, 468 ± 205, 513 ± 151, and 450 ± 162 MPa for those with 0, 0.09, 0.37, and 0.62 wt% carbonate, respectively. No significant decrease in strength was found for hydroxyapatite single crystals both in water and after the immersion in the medium. However, the strength of OH-carbonated hydroxyapatite single crystals decreased significantly by 23 to 43% in water in proportion to the carbonate content. The strength of single crystals with 0.37 and 0.62 wt% carbonate decreased significantly, even after the immersion in the medium. Therefore, hydroxyapatite single crystals are superior to OH-carbonated hydroxyapatite single crystals as a biomaterial for a load-bearing purpose.

Bending strength of synthetic OH-carbonated hydroxyapatite single crystals

Although hydroxyapatite (HAP) is applied to medical implants because of its biocompatibility, no data on mechanical strength of HAP single crystals were yet available, partly due to the difficulty in obtaining sufficiently large single crystals. In the present study the bending strength of OH-carbonated hydroxyapatite (CHAP) single crystals containing carbonate of 0.09 CO2 wt % prepared hydrothermally was determined in three-point bending tests. The three-point bending tests were performed using a modified ultra micro-hardness tester with a span of 380 micrograms and a bending direction of <210>. The CHAP single crystals were broken in air, water, and air after immersion in alpha minimum essential medium (alpha MEM) + 10% fetal bovine serum (FBS) for 3 weeks. The average bending strength of the CHAP single crystals was 468 +/- 205, 361 +/- 199 and 501 +/- 212 MPa in air, water, and air after immersion in alpha MEM + 10% FBS, respectively. In all cases the maximum strength at each crystal thickness value decreased in inverse proportion to the thickness.

Effect of gadolinium content on the thermal volume change of Ba4Na2Nb10O30− Ba3NaGdNb10O30 solid solutions at ferroelectric phase transition temperature

For sintered samples of Ba3+x Na1+xGd1−xNb10O30 (1 ⩾x ⩾ 0), the effect of the addition of gadolinium to barium sodium niobate (BNN,x = 1, tungsten bronze type) was examined by differential scanning calorimetry (DSC) and X-ray powder diffractometry. The volume change (i.e. especially the change ofc-axis length) at the ferroelectric phase transition temperature (Tc< 590 dg C) decreased with the increasing gadolinium content. This result suggests that the addition of gadolinium or other lanthanide elements to BNN is possibly effective to obtain an uncracked single crystal with the Czochralski technique. The DSC indicator method is useful to determine the relative magnitude of volume change atTc for the same type of sample series, a method which is much easier than the dilatometer method. The relation between the DSC peak area and the volume change of unit cell atTc is discussed from the thermodynamic viewpoint.

Surite; its structure and properties

Abstract Surite has been reported to be a mineral that intercalates cerussite-like materials in a smectite interlayer. However, the chemical analysis and infrared absorption spectra indicate that the interlayer material has the composition of Ca0.5OH·2PbCO3. A one-dimensional Fourier synthesis of electron density for acid-treated surite shows that the 2:1 layer of surite has the structure of a general smectite (the distance between the Si plane and the apical O atom plane is about 1.6 Å ). Moreover, the one-dimensional Fourier synthesis method showed that the crystal structure of surite is a 2:1 dioctahedral smectite interlayered with basic lead calcium carbonate.

A nickel hydroxide-vermiculite complex : preparation and characterization

A nickel hydroxide-vermiculite complex (NHVC) with csinβ = 1.41 nm and particle sizes from 0.075 to 0.15 mm was obtained hydrothermally by adding nickel nitrate solution to vermiculite from Transvaal, South Africa. The quantity of nickel hydroxide included in NHVC was controlled by adjusting the concentration of the nickel nitrate solution. The thermal behavior of NHVC at 450°C or above was independent of the Ni content. However, small differences exist in the dehydration behavior of NHVC below 450°C. One-dimensional Fourier electron density analysis of the NHVC structure containing 2.43 mol of Ni per half unit cell showed that Ni cations occupy the interlayer of NHVC, and 10% of the total Ni cations is in the ditrigonal cavity of the basal-oxygen plane of the tetrahedral sheet.

GROWTH OF UNCRACKED BARIUM-SODIUM NIOBATE CRYSTALS

It is known that cracking occurs in Barium-Sodium Niobate, Ba4Na2Nb10O30 (BNN), during Czochralski (cz) growth. This is due mainly to lattice distortions associated with the ferroelectric phase transition. We have studied the cz crystal growth condition for BNN without cracking, and found that high quality single crystals of BNN without cracking can be grown by using Gd-doped starting melt, i.e., Ba4Na2Nb10O30-Ba3NaGdNb10O30 solid solution. In order to confirm the effect of Gd doping on the crystalline quality, Gd concentrations were measured by ICP for both the cz single crystal sample and the starting powder material. Gadlinium concentration in the as-grown crystal was about 0.195 mol %, nearly the same as that (2.0 mol %) in the starting material. Dielectric constant along c-axis, e33, was measured at temperatures from 300 K to 870 K. The experimental result revealed that e33 of the single crystal is about two times larger than that of BNN single crystal without Gd impurity in the temperature range from 300 K to 650 K.

Phase-Matching of Optically Second-Harmonic Generation in the Single Crystals of Gd- and La-Added Barium Sodium Niobate

Optically microscopic observation, measurements of the phase-matching temperature of second-harmonic generation (SHG) and evaluation of the SHG conversion efficiency were carried out for three kinds of single crystals: barium sodium niobate (BNN), La-added BNN [BN(La)N] and Gd-added BNN [BN(Gd)N]. The best crystalline-quality crystal was [BN(Gd)N] and the crystal showing the highest SHG conversion efficiency was also [BN(Gd)N]. The phase-matching temperatures were about 120°C and 160°C. Some discussion was given on the SHG phase-matching.